Recently, information processing devices such as a word processor, a personal computer, a facsimile, etc., have rapidly become widespread. With the widespread development of the information processing devices, the necessity of making hard copies of the outputs from these terminals has been increased. Various recording systems such as a heat-sensitive recording system, a heat transfer system, an electrophotographic system, an ink jet recording system, etc., have been practically used as a recording system for such a hard copy.
However, in the recording system which is practically used at present, the once recorded content of an output is semi-permanently kept and a paper used for recording cannot be used again. Thus, a large amount of recording papers have been consumed at the terminals of various information processing devices. Recently, the recognition for the preservation of the environment of the earth and for the conservation of natural resources has been increased and it has been required to use materials capable of recycling as the recording media used for printers. However, a recording paper capable of repeatedly conducting an image formation and erasing is not yet obtained at present.
Furthermore, a payment by a credit card, a prepaid card, etc., has been popularized and a so-called cashless system is being actively used. The information recorded on such a credit card, a prepaid card, etc., is generally a magnetically recorded information, an optically recorded information, an IC memory, etc. It has also been desired to convert the information which is recorded on such a card and cannot be detected visually into a visible information for the convenience of users.
From such a standpoint, a recording sheet having formed thereon a reversible heat-sensitive recording material comprising a binder having dispersed therein an organic low molecular weight material such as a higher fatty acid, etc., as the heat-sensitive recording layer is proposed and is being practically used (European Patent No. 868). However, the recording sheet records an information or an image by heating as a white turbid state in a transparent state by the difference in the sizes of crystals and hence in principle, an information or an image having both a sufficient density and a sufficient contrast is not obtained in the recording sheet and further it is impossible to obtain a colored information or image.
PCT Patent Publication (unexamined) WO/11898 proposes a composition capable of coloring and erasing an image by using an amphoteric compound having a hydroxyl group and a carboxyl group and also having inevitably an amino group as a pyridine derivative and conducting a chemical reaction while controlling a heat energy. When the composition is coated on a substrate to form a recording sheet, the recording sheet is colored by heating with a thermal head, etc., for a short period of time (from few milli-seconds to few tens milli-seconds) and decolored by heating for a long period of time (about several seconds). The invention of the above-described PCT patent publication can also provide a reversible color heat-sensitive recording medium having a good visibility and capable of repeatedly coloring and decoloring.
However, the composition described in WO/11898 described above has the disadvantages that when the colored records are allowed to stand under an ordinary storage condition, the record is decolored with the passage of time, and also at erasing the colored images by heating, color residues are formed to some extent and the recorded color images cannot be completely eliminated.